1. Field of the Invention
The present invention relates to a system and a method for testing semiconductor devices such as transistors and diodes, and more specifically, to an automatic classification system and method for automatically classifying semiconductor devices by determining current-voltage characteristics (hereinafter referred as xe2x80x9cthe I-V characteristicsxe2x80x9d)thereof with small memory capacity, as well as to a recording medium which is readable by a computer, storing the program for causing the automatic classification system to function and executing the method.
2. Description of the Related Art
At the final stage of manufacturing of field effect transistors (FETs), an examination test of the FETs is generally required. Conventionally, in the examination test, the drain-leakage current of FET is detected by a current measuring unit or a current tester. In the measurement, a specific voltage of predetermined level is applied between source and drain electrodes of FET with gate electrode being open, and the drain-leakage current is measured at the specific voltage. Then, the measured drain-leakage current at the specific voltage was compared with a standard value, and the FET having drain-leakage current not satisfying the standard value is rejected as defective device.
In such a testing, it is possible to screening out defective FET from acceptable FET, according to the detected drain-leakage current measured at the specific voltage, but it is not possible to determine the reason why the defective FET have been resulted to be poor in the manufacturing process. Or, it is not possible to determine the pattern of a characteristic-curve which shows how the drain-leakage current is related to the voltage applied between source and drain electrodes. Therefore, in order to examine the failure mode of the defective devices for further qualification, an I-V curve tracer is required to obtain the I-V characteristics, in addition to the screening device measuring only the drain-leakage current at the specific voltage. The I-V curve tracer measures again the drain-leakage currents of defective FETs supplying sawtooth voltages between source and drain electrodes of each of defective FETs, continuously changing the supply voltages in a certain voltage span. In this case, the classification task of the I-V characteristics must be done manually.
Such a method of manual classification using the results of continuous measurement by the I-V curve tracer requires a tremendous amount of time and labor for classification. In addition, as it takes a long time to analyze the failure modes of the defective devices, it is difficult to quickly respond in case such a failure or trouble is found in the semiconductor device.
Further, since the measurement is carried out with supply voltages continuously changing in the certain voltage span, by the I-V curve tracer, a vast amount of memory capacity has been required for storing the measured data with continuously changing supply voltages.
The present invention is intended to solve the problems described above and one object of the present invention is to provide an automatic semiconductor device classification system capable of significantly reduce time required for measuring, storing, calculating and classifying I-V characteristics of many semiconductor devices respectively located in respective exposure areas, step-and-repeatedly arranged on a surface of a large-diameter semiconductor wafers so as to manufacture a plurality of semiconductor devices.
Another object of the present invention is to provide an automatic semiconductor device classification system, capable of classifying I-V characteristics curves of the semiconductor devices without using the I-V curve tracer or the equivalent measuring instruments.
Yet another object of the present invention is to provide an automatic semiconductor device classification system, capable of reducing the number of required testing steps and the xe2x80x9cturn-around-timexe2x80x9d of the semiconductor devices.
Yet another object of the present invention is to provide a relatively low cost automatic semiconductor device classification system, having a simple system organization and is able to reduce the computer resource (i.e. memory capacity)required for the automatic classification of I-V characteristics.
Yet another object of the present invention is to provide an automatic semiconductor device classification system, having a simple system organization and is able to determine the I-V characteristics of a plurality of semiconductor devices in respective chip areas arranged on surfaces of semiconductor wafers, and thereby produce a classification map of the semiconductor wafer showing the respective I-V characteristics easily and quickly.
Yet another object of the present invention is to provide an automatic semiconductor device classification system, which is capable of significantly reducing time and labor required for analyzing failure modes of semiconductor devices.
Yet another object of the present invention is to provide an automatic semiconductor device classification system in which a shorter development period of a new-type semiconductor device and a quicker remedy response to a failure or trouble occurred in the device can be easily achieved.
Yet another object of the present invention is to provide a method for automatically classifying semiconductor devices in which the amount of time required for sorting-out or for classifying the I-V characteristics of a large number of semiconductor devices can be significantly reduced.
Yet another object of the present invention is to provide a method for automatically classifying semiconductor devices in which the I-V characteristics of the semiconductor devices can be classified into predetermined categories, without using the I-V curve tracer or the equivalent measuring instruments.
Yet another object of the present invention is to provide a method for automatically classifying semiconductor devices in which the turn-around-timexe2x80x9d of the semiconductor devices can be reduced.
Yet another object of the present invention is to provide a method for automatically classifying semiconductor devices in which the amount of data required for the computation of the automatic classification can be significantly reduced.
Yet another object of the present invention is to provide a method for automatically classifying semiconductor devices in which a classification map of the I-V characteristics of semiconductor devices arranged on surfaces of semiconductor wafers can be quite easily produced.
Yet another object of the present invention is to provide a method for automatically classifying semiconductor devices in which the amount of time and labor required for analyzing failure modes of the semiconductor devices can be significantly reduced.
Yet another object of the present invention is to provide a method for automatically classifying semiconductor devices in which a shorter development period of a new-type semiconductor and a quicker response to failures or troubles can be easily achieved.
Yet another object of the present invention is to provide a recording medium which is readable by a computer and which stores a program for the automatic classification of I-V characteristics, the program being suitable for operating the aforementioned automatic classification system and the method of the semiconductor devices.
In order to achieve the objects described above, a first aspect of the present invention inheres in the automatic semiconductor device classification system comprising a current measuring unit, a data memory, and a processor connected to the data memory and the current measuring unit. The current measuring unit includes a voltage controller and an ammeter. The current measuring unit measures discrete current vs. voltage relations (hereinafter referred as xe2x80x9cthe I-V relationsxe2x80x9d) between predetermined electrodes of a semiconductor device, using discrete output voltages of the voltage controller. The data memory stores the discrete I-V relations, a first control voltage, a first threshold current value at the first control voltage, a second control voltage which is larger than the first control voltage, and a second threshold current value at the second control voltage. The processor includes an acquisition circuit which obtains the decision current values, a comparison circuit which compares the decision current values with the threshold current values and is connected to the acquisition circuit, and a classification circuit which execute the pattern-determination and classification and is connected to the comparison circuit. In the acquisition circuit, the first decision current value at the first control voltage and the second decision current value at the second control voltage are obtained using the discrete I-V relations stored in the data memory. In the comparison circuit, the first decision current value is compared with the first threshold current value stored in the data memory and the second decision current value is compared with the second threshold current value stored in the data memory. Finally, in the classification circuit, a pattern of the curve representing an approximate I-V characteristic between the predetermined electrodes is determined on the basis of the comparison results obtained by the comparison circuit, and classification into predetermined category is performed according to this determination. The acquisition circuit, the comparison circuit and the classification circuit may have the dedicated hardwares respectively, or may comprises a general purpose computer system in which the respective functions of the circuits are defined by the instructions given by a software program.
The xe2x80x9csemiconductor devicexe2x80x9d tested by the automatic classification system according to the first aspect of the present invention may include diodes and transistors. The transistors may include bipolar transistors(BJTs), FETs and static induction transistors(SITs). The diodes may include semiconductor light-emitting devices such as light-emitting diodes(LEDs) and semiconductor laser diodes(LDs). The gate structure of FET and SIT may be an insulated gate structure such as MOSFET, MISFET, a pn junction structure or a Schottky gate structure. High electron mobility transistors (HEMT) having a heterojunction gate may also be included in the transistor having the insulated gate structure. In addition, the xe2x80x9csemiconductor devicesxe2x80x9d of the present invention may further include insulated gate bipolar transistors (IGBTs), gate-turn-off(GTO) thyristors, static induction thyristors(SI thyristors), and MOS composite devices such as emitter-switched thyristors(ESTs). In the present invention, xe2x80x9cbetween the predetermined electrodes of a semiconductor devicexe2x80x9d means couples of electrodes between anode and cathode electrodes of a diode, between emitter and collector electrodes or between emitter and base when I1 less than id1 and id1 less than I2 and I1 less than id2 and id2 less than I2, it is determined to be xe2x80x9cchannelxe2x80x9d. gate electrodes of FET (or SIT), between anode and cathode electrodes of GTO when id1 less than I1 and I1 less than Id2 and id2 less than I2, it is determined to be xe2x80x9csoft break downxe2x80x9d.
According to the automatic classification system of the first aspect of when I2 less than id1 and I2 less than Id2, it is determined to be xe2x80x9cshort circuit failurexe2x80x9d. whether the reverse I-V characteristics between source and drain electrodes of when id1 less than I1 and I2 less than Id2, it is determined to be xe2x80x9chard break down (low breakdown voltage)xe2x80x9d. hard-breakdown characteristics, is automatically carried out and then when id1 less than I1 and id2 less than I2, it is determined to be xe2x80x9chard break down (normal)xe2x80x9d. As the curve pattern showing the approximate I-V characteristics of the semiconductor device can be automatically classified, the discrete I-V relations can be thoroughly measured for a plurality of semiconductor devices periodically arranged on various semiconductor wafers of 6-inch to 12-inch diameters or the like, and thereby the time required for classifying into the predetermined categories can be effectively reduced. Further, as simply the measurement of the discrete I-V relations by the current measuring unit suffices the classification of the semiconductor device, the I-V curve tracer or the equivalent measuring instrument is not necessary any more and thereby the number of required steps during the testing can be reduced. In a case in which the I-V curve tracer is used, a vast amount of memory capacity is required for storing the measured data because the measurement is continuously carried out, being scanned by sawtooth voltage waves. On the other hand, according to the automatic semiconductor device classification system as the first aspect of the present invention, only about 2 to about 10 items of measured data is needed for one semiconductor device and thus the amount of required memory capacity can be significantly reduced. Yet further, a classification map of the approximate I-V characteristics of a plurality of semiconductor devices in respective chip areas arranged on surfaces of semiconductor wafers can be very easily produced because the pattern of the curve showing the I-V characteristics of the semiconductor device can be automatically classified and thus the required computation time per a semiconductor device is reduced (this task is quite long time and labor-consuming when manually done). Yet further, as the amount of time and labor required for analyzing the failure mode of the semiconductor device is significantly reduced, a new-type semiconductor device can be developed in a shorter period and failures or troubles can be repaired or solved with more quickly.
A second aspect of the present invention inheres in a method for automatically classifying semiconductor devices comprises the steps of: (a) setting a first control voltage, a first threshold current value at the first control voltage, a second control voltage which is larger than the first control voltage, and a second threshold current value at the second control voltage; (b) applying a set of discrete measuring voltages between predetermined electrodes of a semiconductor device and measuring discrete current values flowing between the predetermined electrodes during application of each of the discrete measuring voltages; (c) obtaining xe2x80x9ca first decision current valuexe2x80x9d at the first control voltage and xe2x80x9ca second decision current valuexe2x80x9d at the second control voltage, on the basis of the discrete current values measured in step (b); (d) comparing the first decision current value with the first threshold current value and comparing the second decision current value with the second threshold current value; and (e) determining an approximate I-V characteristic between the predetermined electrodes of the semiconductor device on the basis of the comparison results obtained in step (d) and classifying the approximate I-V characteristic into predetermined category.
According to the method for automatically classifying semiconductor devices of the second aspect of the present invention, since the curve pattern representing the I-V characteristics of the semiconductor device can be automatically classified, the discrete I-V relations can be thoroughly measured for each of a plurality of semiconductor devices arranged on surfaces of semiconductor wafers of large diameter, and thereby the time required for classifying into the predetermined categories can be effectively reduced. Further, since only the measurement of the discrete I-V relations by the current measuring unit suffices for the classification of the semiconductor devices, the I-V curve tracer or the equivalent measuring instrument is not necessary any more and thereby the number of required steps during the testing can be reduced. And, only a few items of measured data is needed for calculation and determination of the approximate I-V characteristics of one semiconductor device, and thus the amount of required memory capacity can be significantly reduced. Yet further, a classification map of the approximate I-V characteristics of the semiconductor device can be very easily produced because the required computation time per a semiconductor device is reduced. Yet further, as the amount of time and labor required for analyzing the failure mode of the semiconductor device is significantly reduced, a new-type semiconductor device can be developed in a shorter period and failures or troubles can be coped with more quickly.
A program for realizing the method for automatically classifying the semiconductor devices described as the second aspect of the present invention can be executed by storing the program in a recording medium which is readable by a computer, and then making a computer read out the program (the computer constitutes the automatic classification system described in the first aspect of the present invention). More specifically, a third aspect of the present invention lies in the program stored in the recording medium readable by the computer and which includes the steps of: (a) setting a first control voltage, a first threshold current value at the first control voltage, a second control voltage which is larger than the first control voltage, and a second threshold current value at the second control voltage; (b) applying a set of discrete measuring voltages between the predetermined electrodes of the semiconductor device and outputting a code for instructing measurement of discrete current values flowing between the predetermined electrodes during application of each of the discrete measuring voltages; (c) obtaining a first decision current value at the first control voltage and a second decision current value at the second control voltage, on the basis of the discrete current values measured in step (b); (d) comparing the first decision current value with the first threshold current value and comparing the second decision current value with the second threshold current value; and (e) determining an approximate I-V characteristic between the predetermined electrodes of the semiconductor device on the basis of the comparison results obtained in step (d) and classifying the approximate I-V characteristic into predetermined category. Herein, the xe2x80x9crecording mediumxe2x80x9d may be a main memory unit or an external memory unit of a computer system, as long as it is the medium in which a program can be stored. The xe2x80x9crecording mediumxe2x80x9d may include a semiconductor memory, a magnetic disk such as a flexible disk or a floppy disk, an optical disk such as a compact disk (CD)-ROM, a magneto-optical(MO)disk, and a magnetic tape such as a cassette tape, and an open reel tape.
Other and further objects and features of the present invention will become obvious upon an understanding of the illustrative embodiments about to be described in connection with the accompanying drawings or will be indicated in the appended claims, and various technical advantages not referred to herein will occur to one skilled in the art upon employing of the invention in practice.